Means to improve center to edge uniformity of electrochemical mechanical processing of workpiece surface

ABSTRACT

An electrochemical mechanical process for electroplating or electropolishing a conductive surface of a wafer is provided. The conductive surface of the wafer is touched by a polishing surface of a compressible pad while a process solution flows through the pad and a potential difference is maintained between the conductive surface and an electrode. The pressure between the polishing surface and a central region of the conductive surface is increased by applying a shaping process to either the conductive surface or the pad.

RELATED APPLICATIONS

This application claims priority from Provisional Patent ApplicationSer. No. 60/462,919 filed on Apr. 14, 2003 (NT-295 P).

This application is also related to U.S. patent application Ser. No.09/511,278 filed Feb. 23, 2000 (NT-102) which is now U.S. Pat. No.6,413,388, the disclosure of which is incorporated herein by reference.

FIELD

The present invention generally relates to semiconductor integratedcircuit technology and, more particularly, to a device forelectrotreating or electrochemically processing a workpiece.

BACKGROUND

Conventional semiconductor devices such as integrated circuits (IC)generally comprise a semiconductor substrate, usually a siliconsubstrate, and a plurality of conductive material layers separated byinsulating material layers. Conductive material layers, orinterconnects, form the wiring network of the integrated circuit. Eachconductor in the wiring network is isolated from the neighboringconductors by the insulating layers, also known as interlayerdielectrics. One dielectric material that is commonly used in siliconintegrated circuits is silicon dioxide, although there is now a trend toreplace at least some of the standard dense silicon dioxide material inIC structures with low-k dielectric materials such as organic,inorganic, spin-on and CVD candidates.

Conventionally, IC interconnects are formed by filling a conductor suchas copper in features or cavities etched into the dielectric interlayersby a metallization process. Copper is becoming the preferred conductorfor interconnect applications because of its low electrical resistanceand good electromigration property. The preferred method of coppermetallization process is electroplating. In an integrated circuit,multiple levels of interconnect networks laterally extend with respectto the substrate surface. Interconnects formed in sequential layers canbe electrically connected using features such as vias or contacts. In atypical interconnect fabrication process; first an insulating layer isformed on the semiconductor substrate, patterning and etching processesare then performed to form features or cavities such as trenches, vias,and pads etc., in the insulating layer. Then, copper is electroplated tofill all the features. In such electroplating processes, the wafer isplaced on a wafer carrier and a cathodic (−) voltage with respect to anelectrode is applied to the wafer surface while a deposition electrolytewets both the wafer surface and the electrode.

Once the plating is over, a material removal step such as a chemicalmechanical polishing (CMP) process step is conducted to remove theexcess copper layer, which is also called copper overburden, from thetop surfaces (also called the field region) of the workpiece leavingcopper only in the features. An additional material removal step is thenemployed to remove the other conductive layers such as the barrier/gluelayers that are on the field region. Fabrication in this manner resultsin copper deposits within features that are physically as well aselectrically isolated from each other. Another important materialremoval technique, especially for wafers with low-k dielectrics, is theelectrochemical polishing (electropolishing) or electrochemical etchingprocess. In electropolishing, an anodic voltage is applied to the wafersurface with respect to a cathodic electrode in an electropolishingelectrolyte. Excess conductor, such as overburden copper is removedwithout physically touching and stressing the interconnect structure. Itis possible to perform electropolishing on a wafer surface whilephysically touching the surface with a pad material. Such techniques arecalled electrochemical mechanical polishing or etching methods.

Some of the adverse effects of conventional material removaltechnologies may be minimized or overcome by employing a planardeposition approach that has the ability to provide layers of planarconductive material on the workpiece surface, as well as planar removalprocesses. These planar deposition and removal processes also haveapplication in thru-resist processes employed in IC packaging. In theseapplications plating is performed into holes opened in resist layersonto seed films exposed on the bottom of each hole or opening.

One technique used for planar deposition and removal of materials iscollectively referred to as Electrochemical Mechanical Processing(ECMPR), which term is used to include Electrochemical MechanicalDeposition (ECMD) processes as well as Electrochemical Mechanicalpolishing (ECMP) which is also called Electrochemical Mechanical Etching(ECME). It should be noted that in general both ECMD and ECMP processesare referred to as electrochemical mechanical processing (ECMPR) sinceboth involve electrochemical processes and physical touching to, ormechanical action on the workpiece surface. All electrochemicaltechniques for material deposition and removal may be referred to as“electrotreatment.”

In one aspect of an ECMPR method, a workpiece-surface-influencing-device(WSID) such as a mask, pad or a sweeper is used during at least aportion of the electrotreatment process when there is physical contactor close proximity and relative motion between the workpiece surface andthe WSID. Descriptions of various planar deposition and planar etchingmethods and apparatus can be found in the following patents and pendingapplications, all commonly owned by the assignee of the presentinvention. U.S. Pat. No. 6,176,992 entitled “Method and Apparatus forElectrochemical Mechanical Deposition.” U.S. Pat. No. 6,534,116 entitled“Plating Method and Apparatus that Creates a Differential BetweenAdditive Disposed on a Top Surface and a Cavity Surface of a WorkpieceUsing an External Influence,” filed on Dec. 18, 2001, and patentapplication Ser. No. 09/961,193 filed on Sep. 20, 2001, entitled“Plating Method and Apparatus for Controlling Deposition onPredetermined Portions of a Workpiece”. These methods can deposit metalsin and over cavity sections on a workpiece in a planar manner. They alsohave the capability of yielding novel structures with excess amount ofmetals over the features irrespective of their size, if desired.

In ECMD methods, the surface of the workpiece is wetted by theelectrolyte and is rendered cathodic with respect to an electrode, whichis also wetted by the electrolyte. During ECMD, the wafer surface ispushed against or in close proximity to the surface of the WSID or viceversa when relative motion between the surface of the workpiece and theWSID results in sweeping of the workpiece surface. Planar deposition isachieved due to this sweeping action as described in the above-citedpatent applications.

In ECMP methods, the surface of the workpiece is wetted by theelectropolishing electrolyte or etching solution, but the polarity ofthe applied voltage is reversed, thus rendering the workpiece surfacemore anodic compared to the electrode. A WSID touches the surface duringremoval of the layer from the workpiece surface.

Very thin planar films can be obtained by first depositing a planarlayer using an ECMD technique and then applying an ECMP technique on theplanar film in the same electrolyte by reversing the applied voltage.Alternately the ECMP step can be carried out in a separate machine and adifferent etching electrolyte or electropolishing solution. This way thethickness of the deposit may be reduced in a planar manner. In fact, anECMP technique may be continued until all the metal on the field regionsis removed. It should be noted that a WSID may or may not be used duringthe electroetching process since substantially planar etching can beachieved either way as long as the starting layer surface is planar.

FIG. 1 is a schematic illustration of an exemplary conventional ECMPRsystem 10 used for processing wafers. In FIG. 1, a WSID 12 havingopenings 14 in it, is disposed in close proximity of a workpiece orwafer 16 to be processed. The wafer 16 is a silicon wafer to be platedwith a conductor metal, preferably copper or copper alloy. The wafer mayor may not have a previously plated copper layer on it. The wafer 16 isretained by a wafer carrier 18 so as to position front surface 20 of thewafer against top surface 22 of the WSID 12. The openings 14 aredesigned to assure uniform deposition of copper from an electrolytesolution 24, depicted by arrows, onto the front surface 22, or uniformelectropolishing from the front surface 22. The top surface 22 of theWSID 12 facing the front surface 20 of the wafer is used as the sweeperand the WSID 12 itself establishes appropriate electrolyte flow andelectric field flow to the front surface 22 for globally uniformdeposition or electroetching. Such an ECMPR system 10 also includes anelectrode 26, which is immersed in the electrolyte 24. The electrolytesolution 24 is contained in a process chamber 25. The electrolyte 24 isin fluid communication with the electrode 26 and the front surface 20 ofthe wafer 16 through the openings 14 in the WSID 12.

It should be noted that the electrode 26 is only schematically shown inFIG. 1. In actual practice, the electrodes are shielded with a particlefilter and other precautions are taken to avoid bubble accumulationunder the WSID and to avoid particles generated on the electrode 26 toreach the surface of the wafer 16. An exemplary copper electrolyte maybe copper sulfate solution with additives such as accelerators,suppressors, leveler, chloride and such, which are commonly used in theindustry. The top surface 22 of the WSID 12 sweeps the front surface 20the wafer while an electrical potential is established between theelectrode 26 and the front surface 20 of the wafer. For deposition of aplanar film such as copper, the front surface of the wafer 12 is mademore cathodic (negative) compared to the electrode 26, which becomes theanode. For electropolishing in the same system the wafer surface is mademore anodic than the electrode.

U.S. application Ser. No. 09/960,236 filed on Sep. 20, 2001, entitled“Mask Plate Design,” assigned to the assignee of the present invention,discloses various WSID embodiments. Also, U.S. application Ser. No.10/155,828 filed on May 23, 2002, entitled Low Force ElectrochemicalMechanical Deposition Method and Apparatus, also assigned to the sameassignee of the present invention teaches means of applying force to thewafer surface by a WSID for ECMPR.

To this end, however, while these techniques assist in obtaining planarmetal deposits or novel metal structures on workpieces and wafers, andother means of planar removal of materials from the wafer surfaces,there is still a need for further development of high-throughputapproaches and apparatus that can yield deposits with better uniformityand high yield, and methods and apparatus that provide more uniformmaterial removal from workpiece surfaces.

SUMMARY

Present invention uniformly planarizes a conductive surface on aworkpiece during an electroplating or electropolishing process.Specifically, in electrochemical mechanical processing (ECMPR) such aselectrochemical mechanical deposition (ECMD) and electrochemicalmechanical polishing (ECMP) or electrochemical mechanical etching(ECME), since the mechanical action applied on the conductive surface onthe wafer assists planarization of the conductive surface, uniformity ofthe applied mechanical action results in uniformly planarized conductivesurfaces.

In one aspect of the present invention, a method of electrochemicalmechanical processing of a conductive face of a wafer is provided. Themethod uses a process solution, an electrode and a compressible padhaving a polishing surface and a backside. The conductive face istouched with the polishing surface of the compressible pad and thepressure between the polishing surface and the conductive face near thecenter of the conductive face is increased. The conductive face isprocessed while maintaining a potential difference and a relative motionbetween the conductive face.

In another aspect of the present invention, a system for electrochemicalmechanical processing of a conductive face of a wafer using a processsolution is provided. The system includes a compressible pad having apolishing surface, a shaping mechanism, and an electrode for applying apotential difference between the electrode and the conductive face asboth the conductive face and the electrode are wetted by the processsolution. The shaping pad is configured to push the conductive faceagainst the polishing surface with more force at the center of theconductive face than the rest of the conductive face.

In another aspect of the present invention, a system for electrochemicalmechanical processing of a conductive face of a wafer using a processsolution is provided. The system includes a wafer carrier holding thewafer, a solution chamber, which has an upper opening, to hold theprocess solution, and a compressible and flexible pad having a polishingsurface and fluid channels. The compressible and flexible pad is placedbetween the upper opening of the solution chamber and the conductiveface of the wafer. The compressible and flexible pad is configured tobow and apply more pressure near the center of the conductive face thanthe rest of the conductive face as the pressure of the process solutionin the solution chamber increases.

In another aspect of the present invention, a system for electrochemicalmechanical processing of a conductive face of a wafer using a processsolution is provided. The system includes a wafer carrier holding thewafer, a solution chamber to hold the process solution, the solutionchamber having an upper opening defined by extendable side walls and acompressible pad. The compressible pad includes a polishing surface andfluid openings and the compressible pad is placed between the upperopening of the solution chamber and the conductive face of the wafer. Asthe pressure of the process solution increases extendable side walls ofthe process chamber push the polishing surface against the conductiveface and apply uniform pressure on the conductive face.

In another aspect of the present invention, a method of electrochemicalprocessing of a conductive face of a wafer is provided. The method usesa process solution, an electrode and a plate, which is flexible andhaving channels. The process solution is flowed through the channels andthe flow of solution results in shaping the plate into a convex shapehaving a top region. A central region of the conductive face is wettedwith the process solution flowing from the top region of the platebefore wetting the rest of the conductive face. The conductive face isprocessed while maintaining a potential difference between theconductive face and the electrode.

In another aspect of the present invention, a method of electrochemicalmechanical processing of a conductive face of a wafer is provided. Themethod uses a process solution, an electrode and a pad which is flexibleand compressible and having channels extending between a polishingsurface and a back surface. The polishing surface is touched with theconductive face and the process solution is flowed through the channels.The flow of solution results in shaping the pad into a convex shape sothat the polishing surface presses near the center of the conductiveface with more force than the rest of the conductive face. Flowing thesolution through the channels applies a pressure onto the back surfaceof the pad. The conductive face is processed while maintaining apotential difference between the conductive face and the electrode.

These and other features and advantages of the present invention will bedescribed below with reference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary conventionalelectrochemical mechanical processing system;

FIG. 2 is an exemplary portion of a wafer surface with a planarconductive layer;

FIG. 3 is a schematic illustration of an electrochemical mechanicalprocessing system of the present invention where a force is applied tothe back surface of the wafer;

FIG. 4 is a graph showing the distribution of the applied force over thewafer surface as the force is applied in the manner shown in FIG. 3;

FIG. 5 is a schematic illustration of interaction between a wafer frontsurface and the workpiece surface influencing device as the centerregion of the wafer back surface is pressed against the workpiecesurface influencing device;

FIGS. 6A–6D are schematic illustrations of various force sources toapply force on the back surface of a wafer;

FIG. 7 is a schematic illustration of the electrochemical mechanicalprocessing system of the present invention where a force is applied tothe back surface of the workpiece surface influencing device;

FIG. 8 is a schematic illustration of the interaction between a waferfront surface and the workpiece surface influencing device as thesurface of the workpiece surface influencing device is pressed againstthe center region of the wafer front surface;

FIG. 9 is a graph showing the distribution of the applied force over thewafer surface as the force is applied in the manner shown in FIG. 8;

FIG. 10 is a schematic illustration of an embodiment of a smartelectrochemical mechanical processing system of the present inventionwhere a force is applied to the back surface of the workpiece surfaceinfluencing device;

FIG. 11A–11B are schematic illustrations of various combinations ofsupport plate and workpiece influencing device having the convexprofile;

FIGS. 12A–14B are schematic illustrations of various thickness plateshaving varying thickness and resulting degrees of bowing under theapplied pressure;

FIG. 15A–15B are schematic illustrations of removing entrapped bubbleswith the present invention by bowing the WSID towards the center of awafer during a process; and

FIG. 16 is a schematic illustration of an alternative electrochemicalmechanical processing system of the present invention where a uniformforce is applied to the front surface of the wafer by a workpiecesurface influencing device.

DETAILED DESCRIPTION

The preferred embodiments will now be described using the example offabricating interconnects for integrated circuit applications. Itshould, however, be recognized that present invention can be used tooperate on any workpiece with various electroplated materials such asAu, Ag, Ni, Pt, Pd, Fe, Sn, Cr, Pb, Zn, Co and their alloys with eachother or other materials, for many different applications such aspackaging, flat panel displays, magnetic heads and such. In the examplesprovided below, the example material that is electroplated orelectropolished will be copper, but it will be understood that othermaterials can instead be used.

In electrochemical mechanical processing (ECMPR) such as electrochemicalmechanical deposition (ECMD) and electrochemical mechanical polishing(ECMP) or etching (ECME), since the mechanical action on wafer surfaceassists planarization of the surface of the wafer, uniformity of thismechanical action is important to obtain uniform process results, suchas uniformly planarized wafer surface.

FIG. 2 shows an exemplary portion of a workpiece 100 or a wafer having afront and a back surface 101 and 102. The wafer 100 comprises asemiconductor substrate 103 and an insulation or dielectric layer 104 onwhich a planar conductive layer 106 such as a planar copper layer isformed in accordance with the process of the present invention. Thecopper layer 106 maintains a uniform overburden thickness over theentire wafer surface. The copper layer 106 is plated to fill features inthe dielectric layer using an ECMD process. Further, in an exemplaryprocess the copper layer 106 may be electropolished using ECMP. Beforethe plating process, the dielectric layer 104 is processed to formfeatures such as vias 108 and trenches 109 and 110. The features 108,109 and 110 and top surface 112 of the dielectric layer, which is oftenreferred to as field region or surface, are lined with one or moreconductive layers such as a barrier layer 114 and a copper seed layer(not shown) before forming the copper layer 106. Interconnects areformed when the copper layer 106 is removed down to the level of fieldregions 112 and the barrier layer covering the field regions is alsoremoved. Over all efficiency of this process depends on the thicknessuniformity of the copper layer 106 over the entire wafer surface. Aswill be described more fully below, the present invention provides amethod of forming a planar conductive layer while maintaining itsthickness uniformity.

During ECMD and ECMP processes, wafers are typically rotated and may bemoved laterally. As can be appreciated, on a rotating wafer surface thelinear velocity due to rotation is zero right at the center of the waferand it increases linearly towards the edge of the wafer in proportion tothe distance to the center. The linear velocity is highest right at theedge of the wafer and it is given by the relationship: V=(2πR/60)cm/second, where “r” is the radius of the wafer in centimeters and “R”is the rotation in revolution per minute (rpm). As can be seen from thisrelationship, velocity “V” increases as the radius of the wafer “r”increases. Mechanical action delivered by a WSID (see FIG. 1) onto wafersurface increases with the relative velocity between the WSID and wafersurface as well as the force applied onto the surface by the WSID.Therefore, in an electrochemical mechanical process, in one method, theuniformity of the mechanical action on the wafer surface may be improvedby keeping the relative velocity between the WSID and the whole wafersurface substantially the same while keeping the force applied by theWSID onto the wafer surface substantially constant. An example of thismethod can be found in U.S. patent application Ser. No. 10/288,558,entitled Electrochemical Mechanical Deposition with Advancible Sweeper,filed Nov. 4, 2002. In that application, a belt type WSID is used forECMD and ECMP processes. The belt WSID or the wafer may be movedlinearly. The high linear velocity of the belt WSID is constanteverywhere on the wafer surface as long as the velocity on the wafersurface due to rpm is much lower than the linear velocity of the beltWSID. For example, if the wafer is rotated with 5 rpm and belt linearvelocity is 100 cm/sec, the linear velocity at the edge of the wafer dueto rpm would be about 5 cm/sec for an 8″ wafer. This is negligiblecompared to the belt speed of 100 cm/sec.

In another method, if the relative velocity between the WSID and thewafer surface is not constant, the force applied by the WSID is adjustedsuch that a higher force is applied onto certain surface regions, suchas the central region of the wafer, where the relative velocity is low.As previously mentioned, in exemplary ECMD or ECMP processes, the waferis rotated and also translated over a stationary WSID surface. If thevelocity of the lateral motion is lower than the motion near the edge ofthe wafer due to rotation, velocity near the center of the wafer wouldbe lower than at the edge. Therefore, additional force needs to beapplied near the center of the wafer to improve process results.

There are various approaches that may be used to apply additional forceon the wafer surface near its center. One such approach involves shapingof the wafer surface. When such shaped wafer surface is pushed against apad structure, its center gets the highest force. An example of shapingwafer 100 while it is processed may be described in connection with FIG.3, which illustrates a partial view of an ECMPR system 200. In FIG. 3,only components such as a wafer carrier 202 and a WSID 204 of the system200 are illustrated for the purpose of clarity. The wafer carrier holdsthe wafer 100 by the back surface 102 while exposing the front surface101 of the wafer to the WSID 204. The wafer is held on a chuck face 203of the wafer carrier.

The WSID 204 may have a compressible layer 206 having a top surface 208.The top surface 208 may be made of a flexible material and may beabrasive or it may contain a polishing pad material. The top surface 208is brought to physical contact with the front surface 101 of the waferduring the ECMD or ECMP processes. The WSID 204 comprises openings 210,such as holes with various geometrical shapes or slits with varyingwidth, or may be made of a porous material that allows a processsolution (not shown) to flow through the WSID and wet the surface of thewafer. The WSID 204 is supported by a support plate 212, which has a topsurface 213 and a back surface 214. The WSID 204 is placed on the topsurface 213 of the support plate 212. The support plate 212 is fixed onside-walls 215 of a process chamber, which is not shown in FIG. 3 butcan be seen in FIG. 1. The openings 210 may continue through the supportplate as support plate openings 216, although size and location of theopenings 216 may be different from the openings 210 in the WSID. Forexample, support plate openings 216 may be made of narrow slits or verysmall holes. Alternately, support plate openings 216 may be larger thanopenings 210. Optionally a flow restrictor such as a filter 218 may beplaced under the support plate. This filter also reduces the number ofparticles that may reach the wafer surface. A process solution 217 inthe process chamber is delivered to the front surface 101 of the wafer100. Process solution 217 flows through the pores of the filter,openings of the support plate and the WSID to reach the front surfaceduring the process.

Referring to FIGS. 3–5, shaping of the front surface 101 of the wafer100 may be performed by applying a force to the back surface 102 of thewafer to deflect the front surface 101. As shown in FIG. 5, as the forceis applied to the back surface of the wafer 100, the wafer bows into theWSID and a higher-pressure interface 219 forms between the center region220 of the front surface of the wafer and the top surface 208 of theWSID 204. This is because the support plate 212 is relatively rigid inthis example and extra compression of the compressible layer of the WSIDin the central region applies higher force to the wafer surface in thisregion compared to the edge region. The size of the pressure interfacedepends on the applied force and depending on the force it may getsmaller or larger. A force source in the wafer carrier 202 may apply aforce to the back of the wafer and cause the wafer to bow into the WSIDand thereby pushing a center region 220 of the wafer 100 in thedirection of the arrow A. The force source may use a pressurized fluid,inflatable membranes, or a mechanism using shims or pins to physicallyapply force to the back surface 102 of the wafer. Application of theforce A, gives the wafer 100 and hence the front surface 101 a convexshape which allows WSID to exert more force on the center region 220than edge region 222 of the wafer 100. In FIG. 4, this can be seen inthe force distance graph 224. As seen in the graph, the force applied tothe center region is higher than the edge region of the wafer.

As shown in FIG. 5, as the force A is applied, the center region ispushed into the WSID 204 by a distance D at the center region 220 and adistance d at the edge region 222. Since the force applied by the WSIDonto the wafer surface is proportional to the distance the surface ispressed into the WSID, as the D distance becomes larger than thed-distance, the force, which is applied to the center region becomeshigher than the edge region. It should be understood that the distancesand the convex shape of the wafer are exaggerated in figures forclarity. In practice the difference between the distance D and distanced may be in the range of 0.1–1 mm for an 8″ wafer or as much as 2 mm fora 300 mm wafer. For the purpose of clarity, openings in the WSID are notshown in FIG. 5.

FIGS. 6A–6D illustrate various configurations of force source. In eachconfiguration edges of the wafer is held by a holding mechanism on thewafer carrier and the force is applied on the back surface of the wafer.FIG. 6A shows a pressurized fluid source 230, preferably air to applypressure to the back surface of the wafer. Fluid source may be in thechuck face 203 of the wafer carrier (see FIG. 3). FIG. 6B illustrates aninflatable member 232 such as a bladder to fill with pressurized air oranother gas to apply pressure. The bladder may be placed between thechuck face and the back surface of the wafer, and attached to the fluidsource 230. FIG. 6C shows a curved object 234, which may be placedbetween the back surface of the wafer and the chuck face to pressagainst the back surface 102 of the wafer to shape it. FIG. 6D shows useof pins 236 configured to have varying length so that more force isapplied to the center region on the back of the wafer. Pins may beplaced in the chuck face and moved by a moving mechanism.

As shown in FIG. 7 in system 200, another method for achieving the sameresult involves applying force to the center region of the WSID 204 andthereby compressing a portion of the WSID more against the center region220. As shown in FIGS. 7 and 8, since the edges of the support plate issubstantially fixed on the side walls of the process chamber, byapplying a force in the direction of arrow B to the back surface 214 ofthe support plate 212, the support plate is bowed towards the frontsurface 101 of the wafer. This way, selected region 240 of the supportplate is brought closer to the center region 220 of the wafer 100 andforms a high-pressure interface 219. The location of the selected region240 is configured to correspond to the center region 220 of the wafer.The bowing effect shown in FIG. 8 and other figures are highlyexaggerated for the purpose of clarity. In practice, during bowing, theselected region may move up a distance only in the range of 0.1 to 2millimeters. As the selected region of the support plate is moved closerto the center region 220 of the wafer, a portion 242 of the compressiblelayer 206 between the center region 220 and the selected region 240 iscompressed between these two surfaces. This, in turn, pushes the topsurface 208 of the WSID against the center region and applies more forceto the center region 220 than the edge region 222. It should be notedthat in this method a relatively flexible support plate 212 may be used.By selecting the thickness and flexibility of the support plate and themagnitude of the applied force, the degree of bowing and the magnitudeof the extra force applied to the central region may be controlled.

Referring back to FIG. 7, the force maybe applied to the support plate212 by exerting more process solution pressure to the back surface ofthe support plate or the filter 218 placed under it. Such pressure givesthe support plate a convex shape. The pressure and thus the magnitude ofthe applied force may be controlled by various means such as flowrestrictors, filters with varying porosity or bleed valves.

One exemplary method of controlling force involves controlling the flowrate of the process solution. Depending on the porosity of the filter218, as the flow rate of the process solution increases, the pressureunder the filter 218 increases. Since the edges of the support plate arefixed, the support plate bows up under increased process solution flowas shown in FIG. 8. It is also possible to increase or decrease theamount of bowing by keeping the flow constant but by using one or morebleed valves that can control the pressure under the filter. In thiscase, by controlling the amount of solution that is bled through thesevalves, the pressure under the filter maybe increased (when valves areclosed restricting the amount of solution bleeding out through them) ordecreased (when valves are opened increasing the amount of solutionbleeding out through them) or kept constant at a predetermined pressurelevel. It should be noted that this process may be automated usingfeedback control as will be discussed later. For the purpose of clarity,openings in the WSID are not shown in FIG. 8.

Another way of controlling the bowing and thus the force on the centralregion of the wafer involves controlling the porosity of the filter. Ata given solution flow rate, filters with smaller pore size would givemore bowing and thus more additional force would be applied to thecentral section of the wafer. As can be seen in the force-distance graphin FIG. 9, the force applied to the center 220 of the wafer is higherthan the force applied to the edge 222.

FIG. 10 illustrates a smart system 250 which can sense the pressureunder the filter element 256 using a transducer. The system 250 includesa WSID 252 supported by a support plate 254. A filter 256 is placedunder the support plate 254. The filter 256 may not be needed if theopenings in the WSID are small enough to keep the cavity 265pressurized. However, presence of the filter is preferable since it alsofilters out any particulates from the process solution before deliveringit to the wafer surface. Process solution 258 enters chamber 260 throughan inlet 262. Differing from the previously described embodiments, apressure-monitoring device 264 such as a pressure transducer monitorsthe solution pressure and, turns on and off a bleed valve 266 to keepthe pressure, and hence the bowing of the support plate at apredetermined desired value. For example, if the flow is set to aconstant value and the pressure in the cavity 265 is higher than thepre-determined value, the bleed valve 266 is automatically opened moreto let more solution out and bring the pressure down to thepre-determined level. Similarly, if the actual pressure within cavity265 is lower than the pre-determined value then the bleed valve 266would automatically close to restrict flow through it and bring thepressure up to the pre-determined level. This way, using feedback andcomputer control a predetermined value for the pressure is selected andkept through the process. Also, by changing the pressure during theprocess, more or less force may be applied on the surface in acontrolled manner. Bowing is a strong function of the choice of filter,flexibility of the support plate and the pressure under the supportplate.

The force may also be controlled by shaping the WSID itself or byconstructing the support plate to make it more or less compliant alongthe diameter of the wafer. Other stiffeners or flexural members can beadded to WSID to produce a force curve of any desired shape forplanarization, especially at the center region.

In this respect, FIGS. 11A–11B illustrate various support plate and WSIDcombined structures to create a bowing effect. As shown in FIG. 11A afirst structure 300 includes a support plate 302 having a curved topsurface 304. A WSID 306 is attached on the curved top surface 304 sothat a top surface 308 of the WSID is in compliance with the curved topsurface 304 of the support plate. As shown in FIG. 11B, support plateand WSID combined structure 310 has a support plate 312 and a WSID 314.In this example, a curved top surface 316 of the WSID is provided usinga curved insert 318. In FIGS. 11A–11B, for the purpose of clarityopenings of the support plates and the WSIDs are not shown in thefigures.

By varying the thickness of the support plate, applied pressure and thesize of the high-pressure interface may be changed. FIGS. 12A–12Billustrate a support plate 320 before and after the application of theforce. The support plate 320 is a thin support plate; therefore, withthe applied pressure it bows more in comparison to a thicker supportplate. This may allow the support plate 320 to apply more localizedpressure and to a smaller area of the wafer.

FIGS. 13A–13B show a support plate 322, which is thicker than thesupport plate 320 described above. Since it is thicker, the supportplate bows less and thereby, it may apply a force to a larger area onthe wafer.

FIGS. 14A–14B illustrate a support plate 324 before and after theapplication of the force. The support plate 324 has a thin section 326;therefore, when a pressure is applied to the thin section, the thinsection 326 protrudes more. This may allow the support plate to applymore localized pressure and to a smaller area of the wafer. Again, thebowing effects in all these drawing are greatly exaggerated to clearlyexplain the invention. For the purpose of clarity, openings in thesupport plates are not shown in FIGS. 12A–14B.

The present invention may also be used for eliminating bubbles that maybe trapped between the wafer surface and the process solution duringelectroplating and electropolishing processes. As shown in FIG. 15A, asa wafer is first lowered towards the WSID 402 and enters the processsolution 403, bubbles 406 may get trapped under the wafer surface 404,especially near the center of the wafer. This is a common problem inelectroplating and electropolishing technologies and is generally due tothe fact that the edges of the wafer may get wetted by the processsolution before its center. If these bubbles stay on the wafer surfaceduring the process, they may generate defects in the forming layers andtherefore they must be removed. As shown in FIG. 15B, when the pressureof the solution 403 is increased to bow the support plate 408 towardsthe wafer 400 at least during the first stage of process when wafer isbeing lowered down towards WSID 402, WSID 402 bows and the solutionflowing from the WSID 402 also takes a convex shape. This way when thewafer is lowered towards the WSID, the central region of the wafer getswetted by the process solution first. Because of the convex shape of theWSID, the solution from the top of the convex shape reaches the centerof the center of the conductive surface of the wafer and wets the centerregion before the solution flowing from the rest of the WSID reaches andwets the rest of the surface of the wafer. This way, since the bubblesare swept away from the center, no bubble entrapment occurs. For thepurpose of clarity, openings in the WSID and the support plates are notshown in FIGS. 15A–15B.

The present invention may also be used to apply uniform force onto thewhole face of the wafer during the process. In this application, a rigidsupport plate can be used so that the support plate moves the entiresurface of the WSID towards the wafer surf ace. One possible embodimentis illustrated in FIG. 16. As shown in FIG. 16, an ECMPR system 500 mayinclude a WSID 502 attached on top of a support plate 504. Edges of thesupport plate 504 are attached to side walls 506 of the process chamber508. In this embodiment, side walls comprises compressible members 510.Compressible members 510 allow support plate to move vertically up anddown with the applied solution pressure in cavity 520. As the solutionpressure in the chamber 508 within the cavity 520 is increased, rigidsupport plate moves towards the wafer surface and the surface of theWSID touches the entire surface of the wafer. The force applied to thesurface of the wafer is uniform at each point on the surface of thewafer. Those skilled in the art would realize that this embodiment maybe used in conjunction with all the other embodiments described so farin this application.

Although various preferred embodiments and the best mode of the presentinvention have been described in detail above, those skilled in the artwill readily appreciate that many modifications of the exemplaryembodiment are possible without materially departing from the novelteachings and advantages of this invention.

1. A system for electrochemical mechanical processing of a conductiveface of a wafer using a process solution, comprising: a wafer carrierholding the wafer; a solution chamber to hold the process solution, thesolution chamber having an upper opening; a compressible and flexiblepad, having a polishing surface and fluid channels, placed between theupper opening of the solution chamber and the conductive face of thewafer, wherein the compressible and flexible pad is configured to bowand apply more pressure near the center of the conductive face than therest of the conductive face as the pressure of the process solution inthe solution chamber increases; an electrode in contact with the processsolution, wherein the system is configured to apply a potentialdifference between the conductive face of the wafer and the electrode;and a control system programmed to control pressure to ensure bowing thepad while relatively moving the conductive face of the wafer and the padinto contact.
 2. The system of claim 1, further comprising a perforatedand flexible support plate placed under the compressible and flexiblepad.
 3. The system of claim 1, further comprising a porous membraneplaced under the compressible and flexible pad.
 4. The system of claim2, wherein a porous membrane is placed under the perforated and flexiblesupport plate.
 5. The system of claim 1, further comprising a pressuresensor placed in fluid communication with the process solution in theprocess solution chamber.
 6. The system of claim 5, wherein the signalof the pressure sensor is fed to a solution flow controller to adjustflow rate of the process solution.
 7. The system of claim 1, whereinelectrochemical mechanical processing comprises electrochemicalmechanical deposition.
 8. The system of claim 1, wherein electrochemicalmechanical processing comprises electrochemical mechanical polishing.